Heme, the prosthetic group of cytochromes is required not only for electron-transport function of these proteins, but also for regulation of their formation. Recent studies show that heme deprivation results in the partial or total loss of several apocytochromes in yeast mitochondria; the mechanisms involved is not yet understood. The goal of this project is to clarify the role of heme in formation of heme proteins by studying the affect of heme on transcription of the genes for apocytochrome c, c1 and for the cytoplasmically synthesized subunits of cytochrome oxidase. Total mRNA from heme-deficient mutant yeast strains, grown under various conditions of heme supplementation will be translated in cell-free reticulocyte lysates. Polypeptide products will be isolated, identified and quantified by immunoprecipitation and gel electrophoretic procedures. If the relevant proteins are not translated in systems containing mRNA from heme-deficient cells, a role for heme in transcription would be indicated. Alternatively, if the proteins are produced, independent of heme availability, it would imply that in vivo loss of apoproteins was the result of proteolytic degradation of unassembled subunits. A role for heme in assembly of holocytochromes and of functional mitochondria would be indicated. The involvement of heme in essential biologic activities of mammalian cells, makes it important to understand the role of this molecule in regulating protein synthesis, and in processes involving assembly and integration of macromolecular structures.